What is the Difference Between Calcitonin and Parathyroid Hormone

The key difference between calcitonin and parathyroid hormone is that calcitonin is a peptide hormone that reduces the serum concentration of calcium, while parathyroid hormone is a peptide hormone that increases the serum concentration of calcium.

The normal serum calcium level in the body is 8-10 mg/dL (2-2.5 mmol/L). Calcium is the most common and one of the important minerals for the human body. The human body needs it to build and fix bones and teeth, help nerve function, facilitate muscle squeeze together, help blood clot and help the heart function. Almost all calcium in the human body is stored in bones. The remaining calcium is present in the extracellular fluid (serum) and tissues like skeletal muscle. Calcitonin and parathyroid hormone are two peptide hormones that are essential to regulate serum calcium concentration.

CONTENTS

1. Overview and Key Difference
2. What is Calcitonin  
3. What is Parathyroid Hormone
4. Similarities – Calcitonin and Parathyroid Hormone
5. Calcitonin vs Parathyroid Hormone in Tabular Form
6. Summary – Calcitonin vs Parathyroid Hormone

What is Calcitonin?

Calcitonin is a peptide hormone secreted by parafollicular or C cells of the thyroid gland in humans and other chordates. It consists of 32 amino acids. Historically, it has also been called thyrocalcitonin. Calcitonin was first purified and discovered in 1962 by Douglas Harold Copp and B. Cheney at the University of British Columbia, Canada. The basic function of calcitonin is to reduce the serum concentration of calcium. Calcitonin has opposing effects to parathyroid hormone (PTH). The importance of calcitonin in humans has not been well established as its importance in other animals. This is because its function is normally not significant in the regulation of normal calcium homeostasis. Moreover, it belongs to the calcitonin-like protein family.

Figure 01: Calcitonin

Calcitonin is formed by the proteolytic cleavage of a larger prepropeptide. This prepropeptide is a product of the CALC1 gene (CALCA). Calcitonin is functional as an antagonist with both PTH and vitamin D3. The secretion of calcitonin is stimulated by an increase of Ca²⁺ ions in the serum, gastrin, and pentagastrin. Calcitonin receptor is a G protein-coupled receptor that is localized to osteoclasts, kidneys, and brain cells. Furthermore, calcitonin assay has medical significance as it is used in identifying patients with nodular thyroid diseases such as medullary carcinoma of the thyroid. In pharmacology, salmon calcitonin is used to treat diseases such as postmenopausal osteoporosis, hypercalcemia, bone metastases, Paget’s disease, and phantom limb pain.

What is Parathyroid Hormone?

Parathyroid hormone (PTH) is a peptide hormone that increases the serum concentration of calcium. It is a hormone secreted by the chief cells of the parathyroid glands, which regulates the serum calcium concentration through its effect on bone, kidney, and intestine. PTH usually influences bone remodelling, which is a process where bone tissue is alternately resorbed and rebuilt over time.

Figure 02: Parathyroid Hormone

PTH is secreted in response to low calcium concentration in the serum. PTH indirectly stimulates osteoclast activity within the bone matrix in order to release more ionic calcium (Ca²⁺) into the blood to elevate the low serum calcium concentration. Moreover, PTH is a polypeptide containing 84 amino acids, which is a prohormone. It is a protein encoded by PTH gene. The molecular mass of PTH is around 9500 Da. Furthermore, there are two receptors for PTH: PTH receptor 1 (bone and kidney) and PTH receptor 2 (central nervous system, pancreas, testes, and placenta).

What are the Similarities Between Calcitonin and Parathyroid Hormone?

• Calcitonin and parathyroid hormone are two peptide hormones.
• Both hormones regulate the serum calcium concentration in different ways.
• Both hormones have specific receptors to which they bind.
• They are proteins made up of amino acids.

What is the Difference Between Calcitonin and Parathyroid Hormone?

Calcitonin is a peptide hormone that reduces the serum concentration of calcium, while parathyroid hormone is a peptide hormone that increases the serum concentration of calcium. Thus, this is the key difference between calcitonin and parathyroid hormone. Furthermore, calcitonin is a protein encoded by the CALC1 gene, while parathyroid hormone is a protein encoded by the PTH gene.

The below infographic presents the differences between calcitonin and parathyroid hormone in tabular form for side by side comparison.

Summary – Calcitonin vs Parathyroid Hormone

Calcitonin and parathyroid hormone are two peptide hormones that regulate the serum calcium concentration. Calcitonin reduces the serum concentration of calcium, while parathyroid hormone increases the serum concentration of calcium. So, this is the key difference between calcitonin and parathyroid hormone.

Reference:

1. “Calcitonin.” An Overview | ScienceDirect Topics.
2. “Parathyroid Hormone.” You and Your Hormones.

Image Courtesy:

1. “Calcitonin Bones” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Major interactions between vitamin D, parathyroid hormone (PTH), calcium and phosphorus around the body” By sportEX journals (CC BY-ND 2.0) via Flickr

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